The present invention relates to the production of signs, and in particular, to the printing of an image for a weather resistant sign such as a license plate.
Vehicle license plates are a challenging problem. They must provide an overall similarity of styling or appearance to enable rapid recognition of license plates issued by various licensing authorities and to inhibit counterfeiting. At the same time, license plates need to provide a distinct, individualized, and unique identifier code or image for each vehicle. In essence, each vehicle requires a custom, short run manufacturing process to incorporate its unique code or image upon a commonly styled license plate blank.
The best known manufacturing process for incorporating the unique image has been stamping or embossing a metallic plate to first provide raised letters or numbers on a plate. Subsequently, the raised letters or numbers are contacted by a liquid ink or paint carried upon a roller or pad. The liquid ink or paint dries to provide a contrasting image which corresponds to the embossed image or raised pattern of the plate. In order to improve the weather resistance, after drying of the ink, the plate is dipped in a liquid clear coating agent (i.e. a solvent born resin or plastic). The resulting plate is relatively durable. However, the embossing and inking process is labor intensive. In the U.S. most of the labor for this process has been prison labor. In other areas of the world, however, private industry or governmental employees are the labor sources for license plate manufacture.
In recent years, many licensing authorities have offered "vanity" license plates at a premium license fee. Such plates allow the licensee to participate in the selection of an attractive or meaningful printed design to be entered upon their license plates. Unfortunately, the production of such "vanity" license plates also entails a significantly greater production cost. Additionally, some licensing authorities desire to reuse previously abandoned identifying codes or images. Preparation of license plates for such nonsequential images also represents a custom manufacturing operation, similar to that required for "vanity" plates. A more versatile and efficient printing process would be useful for preparing regular, nonsequential, and vanity license plates.
Another aspect of the present embossing and liquid inking process is the release of solvent vapor from the drying ink. This solvent release is in addition to solvent released by the dipping and subsequent drying of the protective clear coating layer. The manufacture of large quantities of license plates requires substantial investment in drying ovens and solvent vapor ventilation. Increased scrutiny of possible environmental and health risks associated with various solvent vapors appears to be a trend throughout the world. It would be advantageous to eliminate the generation of solvent vapors from the process of printing license plates.
Many traffic signs and license plates have a retroreflective property which is generally considered desirable in the industry. In such cases, inks or paints have been selected for compatibility with the retroreflective materials. A more versatile and efficient printing process would accommodate a variety of colorants and be compatible with retroreflective components used in license plates and traffic signs.